That's Mr. Mxyzptlk, the fifth-dimensional imp that Superman is pestered by every 90 days when his and our dimensions become aligned. He challenges Superman to make him say his name backwards at least once, and he'll leave. If Superman doesn't, his super-science/magic will make life almost unbearable for The Man Of Steel (not to mention the rest of the world).

Mxy's been around since the very early-1940's. Are you SURE you don't recognize him, Skips?